Modification of the Bligh and Dyer extraction method by addition of EDTA and KCl to the water phase permits quantitative extraction of the inositides, and shows that human platelets are as rich in polyphosphoinositides as rat brain, a tissue known to be heavily endowed with these compounds. The inositides and 5 other heretofore neglected PL of human platelets can be labeled by phosphorous inositide 32 in vitro and all 8 of the labeled lipids can be separated with a single development on formaldehyde-treated paper by a modification of the method of Horhammer et al. We have found that the uptake of 32 phosphorous inositide can be enhanced by modifying the incubation medium in any one of 3 ways: 1. Reducing its osmolarity; 2. Increasing the ratio of Na/K; 3. Addition of succinate. We propose continuing studies on the inositides and the other PL which are labeled by 32 phosphorous inositide in vitro to answer the following questions: 1) Which pathway predominates for biosynthesis of each of the identified PL? 2. What is the link between energy substrate metabolism ATP32 generation and PL biosynthesis in isoosmolar and hypoosmolar media? 3. Does the Na/K ratio influence PL metabolism through redirecting energy metabolism or by stimulating a specific monovalent cation carrier? 4. How do added thrombin and Ca2 ion influence turnover of P32-labeled PL? 5. How does platelet storage affect energy substrate metabolism and P32-labeling of PL? 6. Can inositides bind serotonin? 7. Is there a specific protein which forms a complex with TPI and Ca2 ion?